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Old 13th Sep 2021, 10:59 am   #1
chriswood1900
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Default The Waddington effect and Preventive Maintenance

I was recently reading an article on wartime research by C H Waddington 1905-1975.
He was tasked with improving the performance of Coastal Command the conclusion from Waddington’s research during World War II:
"Maintenance isn’t an inherently good thing (like exercise); it’s a necessary evil (like surgery). We have to do it from time to time, but we sure don’t want to do more than absolutely necessary to keep our aircraft safe and reliable. Doing more maintenance than necessary actually degrades safety and reliability."

My gut instinct is that this effect is noticeable in many areas where items receive scheduled maintenance although the modern tendency seems to be to stretch intervals, I wondered what other forum members experience was in this area.

You can read more here:- https://livingstingy.blogspot.com/20...on-effect.html
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Old 13th Sep 2021, 12:20 pm   #2
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Default Re: The Waddington effect and Preventive Maintenance

The more dismantling/reassembly going on, the greater the likelihood of mistakes/omission/distraction detracting from the desired outcome and becoming counterproductive. Very much a case of striking a careful, rational and informed balance. Halifax V9977.
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Old 13th Sep 2021, 1:59 pm   #3
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Default Re: The Waddington effect and Preventive Maintenance

There are two main philosophies. Design for maintenance design not to need maintenance.

These days stuff does power on self test and tells you when it needs service and what is wrong. Much better than having to strip and rebuild things as a matter of course.

The stuff I designed was not intended to need maintenance and would do 50,000 hours. I hated the need for things like fan filter changes.

Even in WWII the idea of exchange engines on aircraft rather than servicing the engine in the airframe was starting to get established. Gave less downtime and less stressed ground crew
crew.

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Old 13th Sep 2021, 3:44 pm   #4
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Default Re: The Waddington effect and Preventive Maintenance

I have a copy of Sandretto's 1940 book on aircraft radio. It describes the plug-in modular approach to aircraft wireless. Airfields carried a stock standard plug-in modules. An aircraft arriving with a faulty item would have it quickly replaced by a new one, allowing the faulty one to be repaired at leisure and avoiding the need to take the plane out of service while the radio was being fixed.
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Old 13th Sep 2021, 4:35 pm   #5
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Default Re: The Waddington effect and Preventive Maintenance

There was an interesting radio programme on recently about a program that was written to determine whether it made more financial sense to replace items only when they failed in a catering kitchen or whether to re-equip the whole kitchen after a pre-determined time (seven years in this case) regardless. The latter approach was deemed the most effficient and this process has been applied to other areas.
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Old 13th Sep 2021, 4:52 pm   #6
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Default Re: The Waddington effect and Preventive Maintenance

Someone is know used to work for a large German manufacturer of lead acid car batteries. He said that the move to maintenence free ones ( with no removable filling plugs) came about because nobody ever bothered to unscrew them to check the level, they just waited until the battery failed and fitted a new one, so deleting the filling plugs saved money.
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Old 13th Sep 2021, 5:56 pm   #7
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Default Re: The Waddington effect and Preventive Maintenance

But that probably coincided with the growth of the use of alternators with solid-state voltage regulators, capable of better voltage control than the electromagnetic regulators of the dynamo era. Less gassing, less electrolyte loss, less need to check level!
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Old 13th Sep 2021, 7:53 pm   #8
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Default Re: The Waddington effect and Preventive Maintenance

But do alternator regulators perform better than dynamo regulators? No difference in my experience. Generally however, alternator outputs are higher, so less discharged batteries due to leaving some items on instead of off.
But back to the original question. During my time in the pottery industry, it was normal practice for all the temperature control instrumentation to receive a 6 monthly check up. If there was found to be an error in calibration, and the technician corrected it, there was a serious risk of over or under firing, with consequences. I made a simple battery and pair of resistors to give an output of about 15mV, which I would connect instead of the thermocouple before any technician touched any critical controllers. Afterwards I would recheck.
On many factories, problems were certain after such visits.
But it was probably wise to have them checked.
In the case of our Kent Mk. 1 Multilecs, fully mechanical potentiometric instruments, the service was essential, as in the very abrasive area (ground aluminium oxide used for supporting the ware in the kilns), mechanical wear was endemic.
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Last edited by MotorBikeLes; 13th Sep 2021 at 7:54 pm. Reason: Close a bracket.
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Old 13th Sep 2021, 10:50 pm   #9
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Default Re: The Waddington effect and Preventive Maintenance

The deletion of the filler caps on aut....ive lead acid batteries was made possible by the use of calcium as opposed to antimony as a hardening agent in the plate grids. The higher gassing voltage resulting from this change reduced the water loss to negligible proportions at reasonable charging voltages.

In my time as a designer of these systems, I encountered good and bad regulator designs with either AC and DC generators, correct temperature compensation being a frequent shortcoming, together with poor applications engineering. This would often give rise to unsuitably positioned batteries. It's very difficult to properly charge a freezing cold lead acid battery.

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Old 13th Sep 2021, 11:07 pm   #10
kalee20
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Default Re: The Waddington effect and Preventive Maintenance

Quote:
Originally Posted by turretslug View Post
The more dismantling/reassembly going on, the greater the likelihood of mistakes/omission/distraction detracting from the desired outcome and becoming counterproductive.
True. But if dismantling has to happen anyway...?

I'm thinking, if a radio chassis has to come out because 'that' capacitor has gone leaky, it's a necessary repair... but it's also an opportunity to do some preventative maintenance: change other waxies; clean and lubricate the dial drive; etc.
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Old 14th Sep 2021, 12:24 am   #11
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Default Re: The Waddington effect and Preventive Maintenance

I wonder if this depends on where something is on the bath-tub curve? If it's on the upward line near end of life, perhaps maintenance risks ending the life. As surgical comparisons have been used, I can think of two people, both in their mid-eighties who were recommended to undergo "relatively minor" heart procedures to correct problems they were not even aware of until tested by doctors. Neither survived; my dad and Neil Armstrong.
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Old 14th Sep 2021, 4:05 am   #12
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Default Re: The Waddington effect and Preventive Maintenance

HP made a number of test sets for the good old GPO. One unit was about the size of a decent portable scope. They had a control process that had equipment stripped, checked and calibrated rather frequently. In that era the male connector on PCBs where they plugged into the motherboard were formed in the PCB itself, with hard gold plate on the connector pads. The sockets on the mother board had fairly high contact pressure and bifurcated contacts to maintain connection even under the prescribed vibration tests. But every cal cycle had all boards out and back in. In the life of the instruments to that point, they'd easily exceeded the in/out cycle specs of the female connectors.

Their inspection/calibration process wore out the gold plate, and atmospheric acids could get at the underlying copper and produce copper salts. It seemed that most failures in the field were down to the edge connector wear. There would have been some due to their life chucked in the backs of vans, as the boards were shaken slightly in their connectors, but their 'preventative' was the root cause of all that it was supposed to prevent.

With my level of diplomacy, at a meeting about these testers wearing out, I did ask how many generations of vans they'd worn out driving them around. I'm getting the hang of this subtlety stuff, now.

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Old 14th Sep 2021, 9:16 am   #13
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Default Re: The Waddington effect and Preventive Maintenance

In my day job I've had to design solutions to vaguely similar issues to those David mentions above.
Various items of test equipment are required to plug into another unit using the same type of connector as is used in the production system. These connectors are specified for around 500 mating cycles. In order to avoid wearing out the test units, they are fitted with "sacrificial" adaptors made of two connectors back to back that are replaced after a certain number of cycles. In this way, the test equipment's fixed connector effectively has a life of 250000 cycles as it sees 500 mating cycles with 500 different adaptors.

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Old 14th Sep 2021, 9:31 am   #14
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Default Re: The Waddington effect and Preventive Maintenance

During scheduled maintenance and calibration of very expensive equipment that was expected to last 20 years, I saw the maker’s service engineers using rubbers (pencil erasers) to clean all the male edge connectors on the numerous printed circuit boards.

A rubber is made of abrasive and gum. The abrasive damages the relatively soft and very thin gold plating leaving the copper track exposed to corrosion. The gum leaves a sticky residue that attracts dirt.

My level of diplomacy failed.

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Old 14th Sep 2021, 9:52 am   #15
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Default Re: The Waddington effect and Preventive Maintenance

A classic example from the world of mainframe computers...

When disc drives had exchangeable disc packs there was a lot of routine maintenance done to keep the heads aligned correctly. The general error rates were not very good, and often worse after maintenance.

It became apparent that the big problem was trying to keep all the disc drives compatible with each other by aligning to a standard. So we adopted the policy of noting which disc packs were used on which spindles and only using them on the spindle that wrote them in the first place. Then we only adjusted them if they stopped working. The result was a massive reduction in reported errors!

(The only snag then was that if a critical drive broke down we had problems swapping packs around).
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Old 14th Sep 2021, 2:15 pm   #16
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Default Re: The Waddington effect and Preventive Maintenance

Tape drives on computers could be equally annoying. One of my clients had to interchange data with Thames Water in Reading, they had An ICL mainframe and the tapes it wrote - on its 'properly aligned, just serviced' 9 track drives were unreadable on our IBM. In the end we had our IBM field service guys misalign an otherwise unused drive to match the misalignment of the ICL tapes.Happiness returned.
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Old 17th Sep 2021, 10:36 am   #17
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Default Re: The Waddington effect and Preventive Maintenance

The need for relentless regular calibration of items can be a source of considerable trouble with items which don't travel well being sent away and returned by couriers who couldn't care less how delicate they are.

I went on holiday one week and returned to find that someone had sent my precious old Hameg hybrid Analogue / Digital scope away for calibration. It was barely working when it came back and it took me the best part of a day to get it all straightened out again, all mainly caused by rough carriage and inadequate packing both ways. I've since said that on no account does it ever get sent anywhere again.
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Old 17th Sep 2021, 9:25 pm   #18
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Default Re: The Waddington effect and Preventive Maintenance

I have spent a big portion of my working life in mining industry with a responsibility of recording, interpreting and documenting workplace related climate data and toxic gases concentrations. This required the use of several fine, expensive, delicate and calibrated instruments. I took pride in keeping these in best possible condition.
Regulations required annual confirmation of calibration performed by a recognized institution. First fact that I learned that the most intelligent way to do this is to make "correction cards". The guys put the instruments on test benches feeding them with a known medium of pressure, temperature, humidity, contents and concentrations of gases. The readout of the specific instrument would thus form a "correction curve" over the range of valid data.
I.e. using a micro pressure gauge I would read "150 Pa", have a look at the correction card and see that for this readout I'd have to add 7 Pa. 157 Pa would be the true value in this example.
They would never open or touch anything inside the instrument; I just got it back with the information described above or with the remark "readout not reproducable, out of range, not plausible". Then and only then it would be at the time to think of sending in the instrument to the manufacturer for recalibration and/or repair.
Believe it or not, one of my favourites was an 80 years old anemometer. A heavy thing of brass but made to last forever. Imagine that one in a top-modern wind tunnel with a computerized control room!
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Old 17th Sep 2021, 10:18 pm   #19
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Default Re: The Waddington effect and Preventive Maintenance

The cynical side of me says that some managers have things 'serviced' so that they can show that it Was Not Their Fault if something subsequently fails and costs the company alot of money. If someone asks me to 'service' something, the first thing I do is ask them what's wrong with it. 'Nothing' is usually the reply, 'but I can't afford it to break'.
I then explain that the item was probably made by humans.
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Old 18th Sep 2021, 7:42 pm   #20
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Default Re: The Waddington effect and Preventive Maintenance

The "serviced so we showed sue diligence " as a cover-your-arse strategy is a goosd consideration.

Pragmatically, I would never allow anything in my lab/workshop/grab-and-go spares-pool rhat did not have authenticable history that showed it was flight/service-worthy.

If aone of my techs needed to go out on a field job and it wasa winter 05:30 morning and he was grabbing stuff to load into his Land-Rover... I'd consider myself to have failed if any of the gear he grabbed had any kind or inconsistency in its calubration or behavior.

My professional/business reputation always was on the line and if I shipped oout to a client some gear that was obsolete or didn't have the latest software-train release I'd be losing contracts.

The nice thing about the likes of Cisco and HP was trhat they openly published future timescales.

End-of-sale.

End of Hardware-support.

End of Software support.

This was great as a way to 'remind' clients of trhe need for an upgrade.



"I can't support you if you insist on running your corporate infrastructure on obsolete hardware"....

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